Compound Interest Calculator

Compound Interest Calculator

Please enter valid positive values.

Compound Interest Calculator — A = P(1 + r/n)^nt

Compound interest is one of the most powerful forces in personal finance. Our compound interest calculator uses the standard formula to compute exactly how much your investment will grow over time — and shows a year-by-year breakdown so you can see compounding in action.

The Compound Interest Formula

The standard formula is: A = P(1 + r/n)nt

  • A = Final amount (principal + interest)
  • P = Principal (initial investment)
  • r = Annual interest rate (as a decimal; e.g., 8% = 0.08)
  • n = Number of times interest compounds per year
  • t = Time in years

For example, $10,000 invested at 8% annual interest, compounded monthly for 10 years, grows to approximately $22,196 — more than double the original.

Compound vs. Simple Interest

With simple interest, you earn interest only on the original principal. With compound interest, you earn interest on both the principal and the accumulated interest — meaning your returns accelerate over time. The difference becomes dramatic over long periods. $10,000 at 8% simple interest for 30 years yields $34,000. The same amount at 8% compounded monthly yields over $109,000.

Effect of Compounding Frequency

The more frequently interest compounds, the higher the final amount. Daily compounding produces slightly more than monthly, which produces more than annual. For most savings accounts and investments, monthly compounding is standard. The difference between monthly and daily compounding is usually less than 0.1%, but it adds up on large sums over many years.

Frequently Asked Questions

What is the Rule of 72?
The Rule of 72 is a quick mental estimate for how long it takes an investment to double. Divide 72 by the annual interest rate: at 8%, money doubles in approximately 72/8 = 9 years.
How does compounding frequency affect growth?
More frequent compounding (daily vs. annual) results in slightly higher returns because interest is added to the principal more often, creating a larger base for future interest. The effect is most noticeable at higher interest rates.
Does this calculator include regular contributions?
No. This calculator covers a single lump-sum principal. For monthly contributions (like SIP investing), use the Investment Return Calculator on this site.
Is compound interest always beneficial?
For savings and investments, yes — it works in your favor. For loans and credit card debt, compound interest works against you, growing the amount owed faster. This is why paying off high-interest debt quickly is so important.
What interest rate should I use?
Use the rate quoted by your bank or investment platform. Historical stock market averages are around 7–10% per year before inflation. High-yield savings accounts typically offer 4–5% in current conditions.